In recent years, there have been widely used ultraviolet-curing compositions in various fields for reasons of saving energy, saving resources, improving workability and elevating productivity. In the field of processing printed circuit boards, there occurs a shift of the conventional heat-curing ink compositions (for example, solder resist inks and marking inks) to ultraviolet-curing ones for the same reasons.
Screen printing has been widely applied to the formation of resist patterns on printed circuit boards. However, this screen printing method frequently suffers from bleeding, bleed-through or sagging in the printing step, which makes it unsuitable for the recent tendency toward high-density printed circuit boards and surface mounting of parts.
In order to solve these problems, there have been developed photoresists of dry film type and liquid photo solder resists. The photoresists of dry film type have some disadvantages such that they are liable to form bubbles in the step of thermocompression, precarious in heat resistance and adhesiveness and expensive. As the liquid photo solder resists, on the other hand, solder resist ink compositions comprising a partial reaction product obtained from a novolak epoxy resin and acrylic acid as the main component are disclosed in, for example, Japanese Patent Laid-Open No. 208337/1985 and No. 59447/1986. To develop these ink compositions, however, it is necessary to use an organic solvent such as 1,1,1-trichloroethane, trichloroethylene, toluene or cyclohexanone, which brings about some problems in working environment and economy. In order to solve these problems accompanying the use of organic solvents, there has been proposed solder resist ink compositions which can be developed with dilute aqueous alkali solutions. For example, U.S. Pat. No. 5,009,982 has disclosed a resist ink composition comprising a product of reaction between a reaction product obtained from a novolak epoxy resin and acrylic acid with a polybasic acid anhydride as the main component. In the case of this resist ink composition, however, it is necessary to adjust the acid value of the product of the reaction between a reaction product obtained from a novolak epoxy resin and acrylic acid with a polybasic acid to a relatively high level so as to smoothly effect the development with a dilute aqueous alkali solution, which brings about some problems in properties. It also suffers from some disadvantages in procedures such that the drying time should be shortened and that when the ink composition is applied on a substrate and allowed to stand for a long time after drying the solvent, the unexposed part cannot be developed with a dilute aqueous alkali solution. Furthermore, a cured article prepared therefrom has only an insufficient electroless gold plating resistance, which brings about another problem.